t: add tests for diff.renames (true/false/unset)

The underlying machinery is well-tested, but the configuration option
itself was tested only in t3400-rebase.sh.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4001-diff-rename.sh

@@ -27,7 +27,7 @@ test_expect_success 'setup' '
 	Line 14
 	Line 15
 	EOF
-	cat >expected <<-\EOF
+	cat >expected <<-\EOF &&
 	diff --git a/path0 b/path1
 	rename from path0
 	rename to path1
@@ -43,6 +43,50 @@ test_expect_success 'setup' '
 	 Line 13
 	 Line 14
 	EOF
+	cat >no-rename <<-\EOF
+	diff --git a/path0 b/path0
+	deleted file mode 100644
+	index fdbec44..0000000
+	--- a/path0
+	+++ /dev/null
+	@@ -1,15 +0,0 @@
+	-Line 1
+	-Line 2
+	-Line 3
+	-Line 4
+	-Line 5
+	-Line 6
+	-Line 7
+	-Line 8
+	-Line 9
+	-Line 10
+	-line 11
+	-Line 12
+	-Line 13
+	-Line 14
+	-Line 15
+	diff --git a/path1 b/path1
+	new file mode 100644
+	index 0000000..752c50e
+	--- /dev/null
+	+++ b/path1
+	@@ -0,0 +1,15 @@
+	+Line 1
+	+Line 2
+	+Line 3
+	+Line 4
+	+Line 5
+	+Line 6
+	+Line 7
+	+Line 8
+	+Line 9
+	+Line 10
+	+Line 11
+	+Line 12
+	+Line 13
+	+Line 14
+	+Line 15
+	EOF
 '
 
 test_expect_success \
@@ -68,6 +112,21 @@ test_expect_success \
     'validate the output.' \
     'compare_diff_patch current expected'
 
+test_expect_success 'test diff.renames=true' '
+	git -c diff.renames=true diff --cached $tree >current &&
+	compare_diff_patch current expected
+'
+
+test_expect_success 'test diff.renames=false' '
+	git -c diff.renames=false diff --cached $tree >current &&
+	compare_diff_patch current no-rename
+'
+
+test_expect_success 'test diff.renames unset' '
+	git diff --cached $tree >current &&
+	compare_diff_patch current no-rename
+'
+
 test_expect_success 'favour same basenames over different ones' '
 	cp path1 another-path &&
 	git add another-path &&